New method for calcium on the ADVIA analyzer is free from interference of gadolinium-type contrast agents

Recently, Siemens Diagnostics released a new calcium assay (CA_2) based on complex formation of calcium with Arsenazo III dye for use on the three automated, random access ADVIA Chemistry analyzers (1650, 2400, and 1200). We evaluated this method for analytical performance as well as potential interference from gadolinium-containing magnetic contrast agents. With Siemens Chemistry serum and urine controls, 2-levels each, the imprecision for the new method was (n=40 each): within-run and total CV of <2.2 and <3.8%, respectively, over all three platforms. The analytical range/linearity of the method (all three systems) was 1-16 mg/dl (serum or plasma) and 1-32 mg/dl (urine). The new method on all three platforms correlated well with a reference (Inductively Coupled Plasma Atomic Emission Spectroscopy) method (n=61, range 4.03-10.30 mg/dl). The ADVIA 1650 CA_2 method also correlated well with the Roche Modular system((R)) Calcium method. The new method showed <10% interference with unconjugated or conjugated bilirubin (50 mg/dl), hemoglobin (1,000 mg/dl), lipids (1,000 mg/dl), and two magnetic resonance contrast agents containing Gadolinium (OptiMARK((R)) 1 mmol/l and Omniscan 1.5 mmol/l). On the contrary, the Roche Calcium method showed significant negative interference with gadolinium-containing contrast agents. We conclude that the ADVIA Ca_2 method can measure serum, plasma, or urine calcium concentrations accurately and is also free from interferences of gadolinium-containing agents.